Proliferation kinetics of early hemopoietic precursor cells with self sustaining capacity in the mouse, studied with 125-I-labeled iodo-deoxyuridine.

With a new labeling technique in radiation chimeras, an attempt was made to determine the duration of the phases of the stem cell cycle including shortest and mean generation time and to estimate the number of hemopoietic stem cells per unit of bone marrow cellularity. The DNA of bone marrow cells in DNA synthesis was labeled with 5-125I-2'-deoxyuridine. The labeled cells were followed after being transfused into fatally irradiated mice. The stem cells were found to have a half-time of about 4.3 days in the donor mice. The average time in the population, i.e. the turnover time of the stem cells, was 6.2 days. The half-time did not change significantly even after transfusion of bone marrow into lethally irradiated recipient mice. Tritiated thymidine (3H-TdR) suicide technique revealed that bone marrow stem cells seeding to the spleens and to the femurs of lethally irradiated recipients behaved differently--S-phase in cells seeding to femurs being shorter. The radiosensitivity of stem cells in S-phase had a D0 of 80 rad whereas stem cells distributed throughout the whole cell cycle had a D0 of 185 rad. The respective extrapolation numbers were 1.23 and 1.14. It is calculated that 2--7% of all nucleated bone marrow cells belong to self renewing stem cell populations. The method described provides a new approach for the study of hematological stem cells.